Metal container coated with a composition comprising an acrylic polymer latex, melamine formaldehyde resin and a phenol formaldehyde resin

ABSTRACT

Water borne, water dilutable metal can coating compositions containing (A) an acrylic polymer latex including an alkyloxymethylacrylamide or -methacrylamide monomer, (B) a melamine/formaldehyde resin, (C) an alkanolamine treated phenol/formaldehyde resin, (D) a lubricant and (E) a defoamer in a water or water/organic solvent mixture are provided. These compositions cure between 15 seconds and 1 minute at moderate can coating cure temperature and permit faster can coating machine speeds on Rutherford can coating machines.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 604,678, filed Oct. 29, 1990,now U.S. Pat. No. 5,043,380.

FIELD OF THE INVENTION

This invention relates to coating compositions for metal containersintended for packaging beverage and food products. More particularly,this invention provides processable water-borne EPA and FDA compliant,metal container coating compositions for containers which are intendedto hold beverages such as beer, soft carbonated drinks and foodproducts. Such containers are required to maintain a high lubricity, lowcoefficient of friction, non-coloring, high gloss and high clarity canappearance surface during the packaging process where the cans will besubjected to post-coating high-temperature pasteurization and/orsterilization processes in retort (pressure cooker-type) waters thatvary in pH from about 5 to about 10.5. In addition, the coating must becapable of withstanding oxidative attack over a wide variety oftemperature and atmospheric conditions for relatively long periods oftime (good shelf life).

BACKGROUND OF THE INVENTION

Metal containers for foods and beverages are generally made fromaluminum, tin-free steel, blackplate and tinplate steel, (which is coldrolled steel sheet coated with a thin layer of tin). Because such metalcontainers are subject to air oxidation or rusting and to corrosioncaused during the pasteurization and sterilization of the beer, sodapop, and various food products which are packaged in such containers,organic reactant polymer coating compositions are used to protect themetal from chemical attack and to protect the food products from thedeleterious byproducts of chemical attack. Due to their potentialcontact with food products, such coatings present additional problems oftoxicology and taste considerations.

Christenson et al. U.S. Pat. No. 4,097,438, as well as the patentreferences cited therein, refer to some of the problems of can coatingfor beverage and food product operations, and disclose water-basedcoating compositions for use as coatings for metal containers intendedfor beverage packages. In the Christenson '438 patent, the polymer ismade in the absence of a mercaptan so that the polymer in the coatingcomposition will not influence the taste of the beverage product in thepolymer coated can. The Christenson U.S. Pat. No. 3,243,139 refers tocan coating composition polymers made with mercaptans. Other of thepatents listed in the Christenson '438 patent disclose coatingcomposition polymers made in organic solvent media, but none of suchpatents recite all of the requirements of this invention.

Brown et al. U.S. Pat. No. 4,195,006 refers to Christenson et al. U.S.Pat. 3,991,216 which claims metal containers coated with thecompositions claimed in Christenson et al. 4,065,415, among others, butdistinguishes the Christenson '216 and '415 patent compositions in thatthe Brown et al. '006 patent adds 20 to 45 percent of acrylonitrile ormethacrylonitrile monomer to its polymer ingredient of its coatingcomposition, and is thus farther removed from the compositions of thisinvention.

McFadden U.S. Pat. No. 4,272,621 discloses water thinable coatingscompositions of aminoalkylated polymers, polyepoxides and water miscibleorganic solvents made water soluble by acidification with hydrobromicacid or a mixture of hydrobromic acid and hydrochloric acid to provideimproved polymer cure rates, but the McFadden '621 patent does notdisclose the components of this invention.

An ideal aqueous coating composition, from the perspective of food andbeverage manufacturing would meet the following criteria:

1) formulated from FDA-approved materials,

2) fast curing at low temperatures,

3) high solids,

4) clean, color-free, shiny coating,

5) cured coating should provide tack-free surface with frictionalcharacteristics permitting easy movement in automated can-fillingequipment,

6) cured coating should be stable when subjected to high-temperatureprocessing utilized to pasteurize or sterilize foods and beverages,

7) cured coating should be stable when subjected to high temperatures inboth acid and basic environments,

8) coating should be capable of adhering to a wide variety of surfaces,including printed and decorated can surfaces,

9) coating should exhibit good shelf life under a variety of atmosphericconditions.

Those in the art would prefer to have can coating polymer compositionsthat satisfy all of the required test parameters, instead of just someof them as well as permit faster can coating machinery speeds. QualityControl tests are made on can coated with these compositions andinclude:

1. Check the can coating gloss and appearance vs. a standard (apreviously approved standard batch of these compositions). The coated cashould have high gloss and clarity, good wetting and adhesion propertiesequal to the standard.

2. MEK (methyl ethyl ketone) rubs: approximately 50+/-10. The actualnumber is recorded. This test estimates the can coatings degree of cure(reaction).

3. Mobility: The Altek Coefficient of Friction (COF) test results aretaken,

a. <0.07 after wash coat bake.

b. <0.07 after additional 3 min.@400° F. PMT inside spray coating bake.

c. <0.08 after additional 10 min.@400° F. TOT overbake.

4. 90 minutes@250° F. Process Resistance test

a. in Deionized Water

b. in Deionized Water adjusted to pH 10.5 with sodium hydroxide (NaOH).

Test can coating against a standard. The coating on the test can shouldexhibit no delamination or loss of adhesion; can may exhibit slightblush equal to standard in both media.

It is an object and purpose of this invention to provide thermosetorganic polymeric metal can coating compositions of this nature thatwith only slight compositional variation:

(a) can be applied in accordance with known can coating methods such asby wash coat, spray coat, curtain coat, roll coat, or in Rutherford cancoating machines at substantially faster ca coating line speeds than ispossible with prior can coating compositions,

(b) will not produce an unacceptable color upon curing and will curefaster at lower bake temperatures, approximately 1 minute at 350° F. PMto 15 seconds at 400° F. PMT (PMT means peak metal temperature),

(c) will be compliant with EPA and FDA regulations in their manufactureand use in can coating operations, and in their association withbeverage and food filling operations which follow, to obtain a cancoating that upon curing will possess a sufficiently hard polymeric filmsurface to prevent can rub or contact marks and be sufficientlycolor-free to make for an acceptably appearing coated can while at thesame time said coating will be open or permeable enough to permit thelubricant contained in the coating composition to bloom, migrate or moveto the surface of the coating to facilitate a sufficient can mobilityproperty between the coated cans so that the coated cans will moveeasily relative to each other and the canning equipment without anysubstantial rub, contact or scratch marks in can processing and beverageand food filling operations,

and which cured polymer coating will also have sufficient "processresistance" properties when exposed to the conventional pasteurizationand sterilization temperatures and the varied pH conditions ranging fromthe acid side pH 5 to basic side pH 10.5 associated with waterstypically encountered in beverage and food filling operations, withoutcoating degradation to ensure an adequate can appearance and productshelf life.

It is also an object of this invention to provide beverage and foodproduct metal cans and metal substrate therefore coated withcompositions of this invention.

SUMMARY OF THE INVENTION

Briefly, this invention provides water dilutable, water-borne, U.S. EPAand FDA compliant, metal container cross-linkable coating compositionscomprising a liquid mixture of

(a) an amide containing acrylic resin latex,

(b) a melamine/formaldehyde-type cross-linking resin,

(c) a base treated phenol/formaldehyde cross-linking resin,

(d) a polymer coating compatible lubricant, and

(e) a defoamer selected from the group consisting of (1) analkyl-branched alkynyl diol having from 10 to 20 carbon atoms, and (2)an aliphatic mineral spirits hydrocarbon mixture having from about 10 to12 isoparaffinic hydrocarbons therein,

said can coating compositions containing therein sufficient liquidselected from the group consisting of water and a water/organic liquidsolvent mixture to maintain the component (A) to (E) dispersibletherein, preferably at a pH between 6.5 and 8.0.

These can coating compositions when applied to metal can surfaces andheated to moderate cure temperature will crosslink sufficiently toprovide cured coatings that will meet the above performance testrequirements within 15 seconds to 1 minute, depending upon the cur heattemperature.

This invention includes metal containers adapted for packaging beverageand food products having at least one metal can surface thereof coatedwith an adherent layer of a coating composition herein set forth.

It has been discovered according to this invention how to make metal cancoating compositions which satisfy the above test requirements, andwhich with only minor or dilutional concentration variations can beapplied by different can coating methods, and which coating compositionscan give faster cure times, at lower temperatures, and which coatingswhen cured on the cans provide the desired process resistance propertiesto the cans during subsequent can filling, pasteurization and/orsterilization operations, at pH extremes ranging from pH 5 to 10.5, foruse in the beverage and food filling/canning industries. Thesecompositions have enabled the speed-up of can coating operations from400 cans per minute on a wash coating equipment to 1200 cans per minuteon Rutherford can coating machines to obtain cans with cured coatingswhich pass the above test requirements.

It is contemplated these coating compositions will be used either a suchor prepared for shipment at a polymer solids percent by weight of from10 to 50, the balance being any possibly partially soluble component (A)to (E) above and water or water/organic solvent mixture carrier. Uponarrival at the can coating site or upon preparation for use thecomposition can be used "as is" or reduced somewhat in concentration forvarnish coat application, e.g., by Rutherford can coating machineapplication methods or the coating composition can be diluted with waterup to approximately 1:1 or more by volume before filling the compositioninto the can coating machinery for wash, spray, curtain or roll coat,applications. A viscosity of the diluted coating composition of about 8to 12 seconds, as measured by the No. 4 Ford cup viscosity measurementtest at standard temperature (77° C.) is generally sought at thebeginning of the can coating operation when the composition is appliedby the curtain can coating procedures. The varnish coat applicationmethods generally involve application of a more concentrated polymersolids coating composition having a viscosity of from about 20 to 150seconds, as measured by the No. 4 Ford cup test method. The viscosity ofthe coating compositions applied by the other mentioned methods would bewithin this viscosity range.

This invention improves the properties of the hereinabove describedcompositions to the point that the resulting coated cans pass all of thestandard can coatings tests. As a result of using these new can coatingcompositions of this invention, can coating personnel can now expect toobtain coated cans which will pass all of the above indicated tests andcoat cans acceptably at faster can coating application speeds on bothRutherford can coating machines, and on wash or curtain coat machines.

These compositions were designed specifically for and are intendedprimarily for use in coating the exterior metal can surfaces. However,we contemplate that these compositions can also be used to coat theinterior surfaces of metal cans.

DETAILED DESCRIPTION OF THE INVENTION

More particularly, the invention provides water borne, water dilutablepolymer combination compositions which are particularly useful forcoating metal can surfaces by various application procedures includingspray, curtain and roll coat applications, or by varnish can coatapplication methods which coated cans are intended for the packaging ofbeverages and food products. These new coating compositions comprise amixture of

(A) from about 10 to about 90 percent by weight of the total solids inthe composition of an acrylic polymer latex containing an acrylamidepolymer component made by using the following monomeric ingredients:

    ______________________________________                                        INGREDIENTS      PERCENT BY WT.                                               ______________________________________                                        (1)   Styrene        3-10                                                     (2)   Ethyl acrylate 0-20                                                     (3)   Butyl acrylate 0-20                                                     (4)   Methyl methacrylate                                                                          5-8                                                      (5)   Methacrylic acid                                                                             3-7                                                      (6)   C.sub.1 to C.sub.6.alkyl-                                                                    0.5-3                                                          oxymethyl-acrylamide,                                                         or -methacrylamide                                                      ______________________________________                                    

based upon the total materials added to the acrylic polymer latexcomponent, in a liquid medium selected from the group consisting ofwater and a mixture of water with an organic liquid solvent, to providefrom about 30 to 35 percent by weight of nonvolatile materials (NVM) insaid polymer latex component,

(B) from about 1 to about 50 percent by weight of the total solids inthe composition of a melamine/formaldehyde source resin, including amethylated melamine/formaldehyde source resin,

(C) from about 0.5 to 50 percent by weight of a base treatedphenol/formaldehyde source resin composition, which phenol/formaldehyderesin has a viscosity of 20 seconds maximum using a No. 4 Ford Cupviscosity test method,

(D) from about 0.1 to about 10 percent by weight of a coating polymercompatible lubricant uniformly dispersible in the total coatingcomposition, and

(E) from about 0.1 to about 5 percent by weight based upon the totalsolids in the composition of a defoamer material selected from the groupconsisting of (1) an alkyl branched alkynyl diol having from 10 to 20carbon atoms and (2) an aliphatic mineral spirits liquid, often calledpetroleum solvent, having C₁₀ to C₁₂ -isoparaffinic hydrocarbons,

said can coating composition containing therein sufficient liquidselected from the group consisting of water and a water/organic liquidsolvent mixture to maintain the components (A) to (E) dispersibletherein. It is preferred to maintain the pH of the composition at a pHof from 6.5 to 8.0, more preferably, between 7.0 and 7.6.

A preferred component (A) of the composition of this invention is one inwhich the acrylic polymer latex component (A) contains about 30 to 35percent of non-volatile material and the acrylic polymer thereof is madefrom about the following proportions of monomers:

6.0 percent, by weight, styrene

3.2 percent, by weight, ethyl acrylate

13.5 percent, by weight, butyl acrylate

3.0 percent, by weight, methyl acrylate

5.0 percent, by weight, methacrylic acid and

1.5 percent, by weight, N-isobutoxymethyl acrylamide

The acrylic polymer latex component (A) of the composition of thisinvention can be any known can coating acrylic polymer. Such polymersare usually prepared from alpha, beta olefinically unsaturatedcarboxylic acidic monomers such as acrylic acid, methacrylic acid,itaconic acid, crotonic acid, mono -C₁ to C₄ -alkyl maleate such asmonomethyl maleate, monobutyl maleate, maleic anhydride, itaconicanhydride, and the like,

and one or more C₁ to C₈ -alkyl acrylate or methacrylate esters such asmethyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate,n-butyl acrylate, isobutyl acrylate, amyl acrylate, hexyl acrylate,heptyl acrylate, 2-ethylhexylacrylate, n-oxtyl acrylate, and the like,and

a vinyl aromatic monomer ingredient such as styrene,alpha-methylstyrene, vinyltoluene (a methylstyrene), or the like.

We prefer to include a C₁ to C₆ -alkyloxymethylacrylamide or-methacrylamide ingredient such as N-isobutoxymethylacrylamide, or anequivalent amount of N-isobutoxymethylmethacrylamide, but otheralkyloxymethylacrylamides and -methacrylamides can be used, e.g., thosehaving methyl, ethyl, n-propyl, tert-butyl, n-pentyl, isopentyl and thevarious hexyl groups in place of the isobutyl group in the acrylic resincomponent (A).

These acrylic polymer latex monomer materials can be combined inconventional proportions and reacted in an organic solvent or mixturethereof, or in an aqueous/alcohol/ether solvent mixture such asn-butanol/butyl ethylene glycol ether or n-butanol/ethylene glycolmonobutyl ether/water mixture in the presence or absence of a mercaptanpolymer chain stopper such as C₁ to C₁₂ -alkyl mercaptan such as methylmercaptan, hexyl mercaptan, octyl mercaptan, n-dodecyl mercaptan, tolimit the molecular weight, if desired, and/or in the presence of aknown reaction initiator such as any of known azobisalkylnitrileinitiators such as azobis(2-methylpropanenitrile) or a peroxideinitiator such as cumene hydroperoxide, tert-butyl hydroperoxide and thelike, by procedures known in the art.

As prepared, the non-volatile materials (NVM) of the acrylic polymerlatex component is generally about 30 to 35 percent by weight,preferably about 32 percent by weight for diluted coat usage, and 34.5%for varnish coat composition.

Other acrylic polymer components useful as components (A) of thecomposition of the invention are known in the art, e.g., as aredescribed in Christenson U.S. Pat. No. 3,037,963, Vogel U.S. Pat. No.3,117,693, Christenson et al U.S. Pat. No. 3,247,139 and Christenson etal. U.S. Pat. No. 4,097,438.

The liquified melamine/formaldehyde source resin component (B) of thecompositions of this invention are known, commercially obtainedmaterials. It can be any known monomeric or polymeric-formmelamine/formaldehyde can coating resin. We prefer to use a liquid-formmaterial referred to as a methylated melamine-formaldehyde resin soldunder the trade product name Resimine® 745, available from MonsantoCompany, St. Louis, Miss. Its resin solids weight percent is said to beabout 100 percent, and the residual formaldehyde percent is said to beless than 0.5 percent, but other similar melamine/formaldehyde resinscan be used. The formaldehyde source used to make these resins can bestandard formaldehyde solution or one of its known polymerized formssuch as paraformaldehyde.

The base treated phenol/formaldehyde resin component (C) of the coatingcomposition of this invention, generally referred to herein as thephenolic resin has been known and used commercially in coatingcompositions for some years. Samples thereof can be obtained from theDexter Packaging Products Division, The Dexter Corporation, 1 WaterStreet, Waukegan, Ill. under the name RP-912. A description of how tomake such a phenol/formaldehyde resin cross-linker is describedhereinbelow.

The base used in the reaction mixture can be any known, cost effectivebase including inorganic bases such as sodium hydroxide, potassiumhydroxide, ammonia, ammonium hydroxide, or an organic base such as atrialkylamine, e.g., trimethylamine, triethylamine, tri-n-propylamine,or a alkylene polyamine such as ethylenediamine, propylenediamine, N, N,N', N'-tetramethylethylenediamine, or an alkanolamine, exemplified inthe next paragraph.

A preferred composition is one in which the phenol/formaldehyde resincomponent (C) is one obtained by combining phenol and formaldehydesource in the presence of an N, N-di C₁ to C₃ -alkyl -C₂ to C₄-alkanolamine as the base. Examples of such amines are N,N-dimethylethanolamine, N, N-diethylethanolamine, N,N-di-n-propylethanolamine, N, N-diisopropylethanolamine, N,N-dimethyl-n-propanolamine, N, N-diethyl-n-propanolamine, N,N-di-n-propyl-n-propanolamine, N, N-dimethylisopropanolamine, N,N-dimethyl-n-butanolamine, N, N-diethyl-n-butanolamine, N,N-dimethyl-isobutanolamine, and the like. N, N-dimethylethanolamine ispreferred.

The lubricant component (D) used in these can coating compositions canbe any of the lubricants known in the art for inclusion in metal cancoating composition purposes. The lubricant should be a polymercompatible substance which will not interfere with the uniformity of thepolymer composition coated surface and still be effective to minimizemar, scratch or contact rub marks on the coated can surfaces. The curingpolymer coating composition must still be sufficiently permeable topermit the lubricant in the coating composition to migrate, bloom ormove to the coating surface to effect a lubricating action betweenadjacent cans and between cans and conveyor equipment as the cans passalong can coating conveyor equipment lines. Examples of lubricantcomponent (D) for the can coating compositions of this invention arewell known, e.g., waxes from various sources such as polyethyleneoligomer waxes, carnauba wax and various natural and synthetic waxmaterials which are commercially available. Trade secret lubricantcompositions such as Michemlube® 160 lubricant which is believed tocontain carnauba wax, and which is sold by Michelman, Inc., Cincinnati,Ohio is a preferred lubricant wax for use as a component (D) accordingto this invention. Other lubricants which can be used to replace all orpart of a wax bearing lubricant component (D) of this invention includevarious silicone oil lubricants, e.g. those of the BYK 300 seriessilicon additives, marketed by BYK Chemical Co. of Germany.

The defoamer component (E) is added to prevent or minimize bubbles whichmight affect the uniformity of the coating on the surface of the can.Any conventional can coating composition defoamer can be used. However,when the new coating composition of this invention is intended to bediluted for use, e.g., as a wash, spray, roll or curtain coat it ispreferred that the defoamer be an alkyl-branched alkynyl diol havingfrom 10 to 20 carbons therein. These are compounds which feature loweralkyl branches on a aliphatic hydrocarbon chain having a triple bondbetween adjacent carbons in the aliphatic hydrocarbon chain and twohydroxyl (alcohol) groups in the molecule. An example of such a defoamercompounds include 2, 4, 7, 9-tetramethyl-5decynyl 4, 7-diol, which iscommercially available under the tradename Surfynol™ 104, available fromAir Products and Chemicals Co., U.S.A.

For use in can coating compositions to be applied as a varnish coat, theabove alkyl-branched alkynyl diol type defoamers can be used.Alternatively, we have found that a defoamer consisting of a petroleumderived mineral spirit liquid believed to consist predominantly of C₁₀to C₁₂ -isoparaffinic hydrocarbons can be used. Examples of thesedefoamers are available from Exxon Corporation, Houston, Tex. and fromEmco Chemical Distribution Co., North Chicago, Ill.

The range of percent by weight of each of the components of these cancoating compositions is influenced by the selected method ofapplication, the polymer cured film weight desired on the coated cans,the intended end use of the cans, whether or not the cans are to havedecoration and/or printing applied directly to the can surfaces beforeor after coating with these compositions, or the cans are to be coveredwith paper labels, and the like.

Preferred ranges of components (A) to (E), in percent by weight of thetotal nonvolatile solids content of the compositions of this inventionfor metal can coating purposes, where the solids content, by weight ofthe compositions comprises 10 to 50 percent by Weight of the solidscontent can be described as containing

(A) from about 60 to 85 percent by weight of the acrylic polymer latex,

(B) from about 15 to 40 percent by weight of the melamine/formaldehydesource resin component,

(C) from about 0.5 to 20 percent by weight of the phenol/formaldehydesource resin component,

(D) from about 1 to 5 percent by weight of the lubricant component, and

(E) from about 1 to 4 percent by weight of the defoamer component.

The above ingredients (A) to (E) are combined either initially uponmixing or after some or all of the ingredients are combined withsufficient liquid selected from the group consisting of water or awater/organic liquid solvent mixture to maintain the components (A) to(E) dispersible therein. The organic liquid component, if used, can beany commonly used organic liquid used in can coating formulation,including at least partially water miscible and water immiscible organicliquids such as n-butanol, isobutanol, tert-butanol, ethylene glycolmonoethyl ether, ethylene glycol monobutyl ether, known in the trade asButyl Cellosolve®, carbon tetrachloride, tetrachloroethylene, and thelike, and mixtures thereof.

In addition, for some can coating purposes these compositions caninclude other ingredients such as coloring dyes where it is desired tocolor the metal can surface, or mineral fillers or pigments where it isdesired to coat the can surface with minor amounts of such materials.Bacteriostatic compounds can also be included, if desired, but such isusually not necessary because residual formaldehyde in the compositionis usually sufficient to counteract any bacterial presence problem.

After at least one metal can surface has been coated with a coatingcomposition of this invention, the coated cans are passed, usually byconveyor equipment through heating stations for a time and at atemperature sufficient to effect a cross-linked cure of the coatingcomposition polymer components in the can surfaces. We have found thatthese coating compositions on can surfaces will cure to an extentsufficient to satisfy the above tests within about 1 minute at 350° F.PMT (peak metal temperature) to about 15 seconds at 400° F. PMT.

The invention is further exemplified by the following detailedPreparations and Examples, which are not intended to be limiting.

PREPARATION 1 Acrylic Latex Component

The acrylic polymer latex formulation component of the coatingcomposition can be prepared in the following manner.

To a clean, dry kettle reaction vessel, blanketed with an inert gas(e.g. nitrogen) to minimize the presence of oxygen, charge 64.3 poundsof butanol and 73.2 pounds of butyl Cellosolve® brand of ethylene glycolmonobutyl ether alcohol and then set the valves attached to the reactionvessel for a direct reflux condition. Then heat the vessel and itscontents to 230° F. and then add 153 grams of Vazo® 64 brand ofazobisisobutyronitrile. Then add 10 percent by volume of a premix #1 of

    ______________________________________                                        POUNDS           INGREDIENTS                                                  ______________________________________                                        30.6             styrene                                                      16.3             ethyl acetate                                                66.4             butyl acetate                                                15.3             methyl methacrylate                                          48.3             methacrylic acid                                             365 (grams)      n-dodecyl mercaptan                                          742 (grams)      Vazo ® 64                                                ______________________________________                                    

Add the remaining 90 percent of the above premix over 90 minutes withstirring while maintaining the temperature at 230°-240° F.

Hold the resulting reaction mixture for 15 minutes at 230°-240° C., andthe cool the mixture to 195° C. Then while maintaining the temperatureof the mixture at 185°-195° F. add over 90 minutes a premix #2 whichcontains the following materials:

    ______________________________________                                        PARTS                INGREDIENTS                                              ______________________________________                                        30.6      lbs        styrene                                                  16.3      lbs        ethyl acetate                                            66.4      lbs        butyl acetate                                            15.3      lbs        methyl methacrylate                                      16.1      lbs        IBMA                                                     365       gm.        n-Dodecyl mercaptan                                      742       gm.        Vazo ® 64 initiator                                  ______________________________________                                    

After all of the above premix #2 has been added, the mixture is held,with stirring, to ensure complete reaction, for 15 minutes. Then, whilemaintaining the temperature of the mixture at 185°-195° C. add in threeportions at 5 minute intervals 117 gm of Vazo® 64 initiator. The mixtureis then held with stirring again for 15 minutes, and then 235 gm ofVazo® 64 initiator is added in four portions at 20 minute intervals. Themixture is held with stirring for 20 minutes and then 117 gm of Vazo® 64initiator is added in four portions at 20 minute intervals. The reactionmixture is held, with stirring, for 60 minutes, and then 59 gm of Vazo®64 initiator and added. The reaction mixture is held for 120 minutes,with stirring. Then, a sample of the reaction mixture is tested todetermine the nonvolatile material content (NVM) of the mixture. The NVMcontent should be 70.4+/-0.25 percent (30 minutes@300° F.).

Then the mixture is cooled at 130°-140° F. and neutralized with 12.3 lbsof N-dimethylethanolamine (DMEA) (to adjust the pH of the mixture to7.1±0.1) followed by dilution with 522.0 lbs of deionized water. Theresulting mixture is mixed for 30 minutes, cooled and filtered.

This component of the composition of this invention is to be stored,shipped and used at temperatures above 32° F.

This acrylic latex component of the coating composition of thisinvention is intended to have the following physical properties whenmanufacture is completed

    ______________________________________                                        Viscosity,            320+/- 30 cps.                                          using RVT#6, 100 RPM at 25° C.                                         Acid Number theoretical                                                                             31.4                                                    Wt./gallon            8.45 +/- 0.1                                            Non-Volatile Materials (NVM)                                                                        32 +/- 1%                                               at 30' @ 300 F.                                                               pH                    7.2 +/- 0.1                                             ______________________________________                                    

This acrylic latex polymer component contains about 6.0 percent styrene,3.2 percent ethyl acrylate, 13.5 percent butyl acrylate, 3.0 percentmethyl methacrylate, 5.0 percent methacrylic acid and 1.5 percentN-isobutoxymethyl acrylamide (N-IBMA) adjusted to contain about 32percent non-volatile material.

PREPARATION 2 Phenolic Resin Component

Into stainless steel chemical reaction vessel equipped with valves andequipment for direct reflux of vapors and liquids from the reactionmixture there is charged 3,414 pounds of deionized water, 5,197 poundsof paraformaldehyde, 2180 pounds of N-dimethylethanolamine, 7,767 poundsof 90 percent phenol in water mixture followed by 63.5 pounds of waterto wash the lines. A 15 inch vacuum is applied. The mixture is heated to160° F. The heat is then removed and the resulting exothermic heat ofreaction is allowed to carry the temperature of the mixture to 185° C.while the vacuum is adjusted to obtain a reflux action at 185° F. Themixture is held with stirring at 185°-188° F. for 60 minutes.

The vacuum is removed and the mixture is cooled to 75°-85° F. A sampleof the reaction mixture is taken to check the non-volatile materials(NVM) content, and adjustment is made, if necessary, to obtain a NVMcontent of about 45 to 55 percent.

The resulting reaction mixture is then run through a filter press into55 gallon drums, and sealed.

The drums are stored promptly at 40° F. maximum until use or shipment.This phenol/formaldehyde resin component material is preferably shippedand stored until use between 32°-40° F.

This phenolic resin has a viscosity of about 20 seconds maximum using aNo. 4 Ford cup method, a weight per gallon of about 9.7+/-0.15 lbs/gal,a color of 7 maximum, a NVM content, after 3 hours at 220° F., of 45-55percent, and a pH of 8.1+/-0.2.

The NVM percentage is determined using a 0.5 gram sample of the phenolicresin product, diluted with methylethylketone (MEK), and a 3 hour bakeat 220° F.

EXAMPLE 1 Wash Coat Can Coat Preparation

A. Using clean stainless steel equipment about 604.831 pounds (71.57gals.) of an aqueous organic acrylic polymer can coating dispersion asdescribed in Preparation 1 containing above about 32 percent ofnon-volatile material is added to the reaction vessel. Then 192.664pounds (23.129 gallons) of deionized water is added slowly with goodagitation of the mixture, and the mixing agitation is reduced to preventexcessive foaming of the mixture (Component A).

Then 38.709 pounds (3.871 gallons) of a commercially available liquidform methylated melamine/formaldehyde resin (Resimine X745, MonsantoCo.) (Component B) is added slowly to the above mixture with goodagitation and mixed for at least 30 minutes before the next step.

Then 11.612 pounds (1.197 gallons) of a liquid form phenolic resinprepared as described in Preparation 2 hereinabove (Component C)adjusted for 50 percent non-volatile materials (NVM) with water is addedslowly with good agitation. The resulting mixture is mixed for at least30 minutes before the next step.

Separately, 3.355 pounds (0.425 gallons) of 2, 4, 7, 9,-tetramethyl-5-decynyl-4, 7-diol defoamer, known as SURFYNOL® 104 -100percent, is mixed with 2.236 pounds (0.331 gallon) of N-butyl alcoholuntil the SURFYNOL 104 is completely dissolved.

Then the resulting SURFYNOL 104/n-butyl alcohol mixture (Component D) isadded slowly to the above batch mixture with good agitation.

Then, 20.645 pounds (2.469 gallons) of a commercially carnauba waxlubricant component (Michemlube 160™) (Component E) is added to thebatch mixture slowly with good agitation. The resulting batch mixture ismixed with good agitation for at least 30 minutes. Then, agitation ofthe mixture is reduced to slow speed and mixing of batch is continuedfor one hour to defoam the batch before sample taking.

The total weight of the mixture should be about 874.052 pounds and thevolume of the mixture should be about 103 gallons. The weight per gallonis about 8.486 pounds. The percent, by volume, of solids is about24.88%. The non-volatile materials is about 28.21 percent. The averageweight per gallon of the volatiles is about 8.109 pound. The coatingcomposition should be shipped and stored between 40° to 90° F.

Our standard or range for coating compositions of this type is makeliquid coating compositions having the following physical properties:

    ______________________________________                                        TEST              STANDARD RANGE                                              ______________________________________                                        Wt./Gal.          8.49 +/- 0.15 lb./gal.                                      Wt. Solids        26.00% +/- 1 percent                                        Vol. Solids       25.0% +/- 2 percent                                         Avg. WPG Volatiles                                                                              8.109 lb./gal.                                              Viscosity         12 +/- 2 Sec.                                               pH                7.1 +/- 0.1                                                 ______________________________________                                    

For wash, curtain, spray or roller coating use, such a composition wouldbe shipped to the place of use and then diluted up to approximately 1:1by volume with water, preferably deionized water, at the place ofcoating application.

A batch of this composition was tested for metal can coat quality whenthe composition was run as a wash coat at a metal can manufacturersplant.

One and one-half truck loads of cans (34 pallets) were wash coated withthis Example 1 composition (diluted at approximately 60:40,coating:water, V/V, prior to addition to the can coating machinery) onthe exterior and sprayed with another proprietary buff coat compositionon the interior. These cans were to be sent to a food company for foodfilling processing.

The coating composition and its can cured condition was consideredacceptable in all respects except that can manufacturer personnelsuggested addition of an odor mask ingredient to this wash coatcomposition. The details of coating were as follows:

    ______________________________________                                        Coating Line #1                                                                             380° F. front zone and                                   Bake/Cure Temp.                                                                             390° F. second zone which gave                                         55" at 375° F. PMT                                       Coating       Example 1 batch, hereinabove,                                                 conc. reduced 60:40, V/V                                        Reducer       Softened city water                                             Reduction     1.5 drums soft water to 2.5                                                   drums Example 1 composition.                                    Film Weight   92.0-91.5 mg./can                                               Refractive Index                                                                            25.0                                                            Can Size      300 × 406 DWI ETP                                         IBO           3' @ 390° F. PMT (8513A39M) 420                                        mg./can                                                         ______________________________________                                         FOOTNOTES:                                                                    PMT means peak metal temperature.                                             DWI means drawn wall and ironed.                                              ETP means electrodeposited tin plate.                                         IBO means inside bake oven.                                              

EXAMPLE 2 Varnish Can Coating Composition

A can coating composition which is particularly useful for applicationto tin coated, steel cans and can substrates, and can ends after thecans are washed, rinsed and dried to remove oils from can manufacturingoperations, to provide coatings on the exterior surfaces of the cans toprotect the can from rusting, rub or contact marks in processing, toprotect the cans during filling operations to hold beer, beverages andfood products that will receive various pasteurization and sterilizationprocesses in retort waters varying in pH from 5.0 to 10.5.

A composition is prepared by mixing the following:

    ______________________________________                                        POUNDS       GALLONS       COMPONENTS                                         ______________________________________                                        640.750      73.649        Acrylic latex dispersion                                                      prepared as in Preparation 1                                                  above.                                             166.371      19.973        Deionized water                                    44.223       4.422         Melamine/formaldehyde resin,                                                  (Resimine, X-745)                                  13,267       1.368         Phenol/formaldehyde resin,                                                    prepared as in Preparation 2                                                  above.                                             9.288        1.472         defoamer - odorless aliphatic                                                 mineral spirits (-CAS #64742 -                                                48-a; Exxon Company - USA)                         17.691       2.116         lubricant (Carnauba wax -                                                     Michemlube 160)                                    891.590      103.000                                                          ______________________________________                                    

The resulting coating composition has a weight per gallon of about 8.656lbs, a percent, by volume, solids content of about 27.37 percent, a NVMcontent of about 31.00 percent, and an average weight per gallon volumeof about 8.223. Our aim is to prepare the varnish coating compositionsto have a weight per gallon of about 8.66+/-0.15 lbs per callous and anNVM content of 30.0+/-1.0 percent.

The pH of this varnish can coat composition as prepared was about7.5+/-0.2.

This varnish can coat composition was tested undiluted as a DWI ProcessExterior Varnish coat for cans at a can manufacturer's plant. It wasconcluded that this Example 2 can coat composition ran successfully as avarnish and bottom rim coating at a line speed of 1200 cans a minute ona Rutherford can coating machine. This composition passed the tests ofthe can manufacturer.

As a result of the performance of this Example 2 in this trial cancoating run, the can manufacturer believes that replacement of the washcoat operations on the exterior of DWI food cans with a varnish coat isfeasible. They have installed Rutherford coaters and pin ovens asreplacements for wash coat operations on two lines in the plant, forusing this composition.

The details of the coating test were as follows:

    ______________________________________                                        Details:                                                                      ______________________________________                                        Coating    Example 2 composition                                              Line       #2 Modified Rotogravure Rutherford 800                                        with Bel Vac Bottom Rim Coater and Ross                                       Pin Oven.                                                          Gravure Roll                                                                             85 QCH                                                             Line Speed 1200 cans per minute                                               Mandrel Speed                                                                            31/4, wraps per can                                                Film Weight                                                                              75, 81, 78 mg./can                                                 Bakes      PIN PAQ not working, temperature tapes                                        only                                                                          A. 40-45 seconds total oven time (TOT)                                        430° F. setting; Approx. 420-425° F. PMT                        B. 40-45' TOT 450° F. Setting. Approx.                                 420-425° F. PMT                                             Cans       211 × 413 DWI ETP(standard B + B can)                        ______________________________________                                    

The coating was run unreduced (not diluted) at an initial cold viscosityof 68 seconds Ford Cup #4. After about 2.5 hours on the coater, thematerial had become quite warm and the viscosity had increased to 120seconds and become foamy. The A. bake variable was run this way.

The high viscosity coating in the Rutherford can coating machine and BelVac coaters was removed and replaced with fresh unreduced (undiluted)coating for the B. bake variable. No foam transfer to the can was seenon either variable, but the flow of of the B. bake variable was better.

EXAMPLE 3 Varnish Coat Formulation

A more recent varnish coat metal can coating composition, similar toExample 2 was prepared generally as described hereinabove using thefollowing proportions of ingredients.

    ______________________________________                                                                              % ON                                    COMPONENT   AMOUNT    NVM      WT %   SOLIDS                                  ______________________________________                                        (A)  Acrylic Latex                                                                            640.734 lbs.                                                                            34.51% 71.87  80.00                                      Water      166.366 lbs.                                                                            .00    18.66  --                                    (B)  Methylated  44.222 lbs.                                                                            100.00%                                                                              4.96   16.00                                      Melamine/                                                                     Formalde-                                                                     hyde resin                                                                    (Resimine ®                                                               X745)                                                                    (C)  Phenol/     13.267 lbs.                                                                            50.00% 1.49   2.40                                       Formalde-                                                                     hyde Resin                                                               (D)  Mineral     9.288 lbs.                                                                             .00    1.04   --                                         Spirits                                                                       defoamer                                                                 (E)  Lubricant   17.691 lbs.                                                                            25.00% 1.98   1.60                                       Michem-                                                                       lube ™ 160                                                                 TOTALS     891.568 lbs.                                                                            --     100.00%                                                                              100.00%                               ______________________________________                                    

The specific gravity of the formulation was 1.037. The weight per gallonwas 8.656 lbs. The NVM was 31.00%. The percent by volume of solids was27.37 percent.

EXAMPLE 4 Wash Coat Formulation

A more recent can coating formulation intended for application to metalcan surfaces by wash coat method, was prepared using the followingproportions of components

    ______________________________________                                                                              % ON                                    COMPONENT   AMOUNT    NVM      WT %   SOLIDS                                  ______________________________________                                        (A)  Acrylic    574.514 lbs.                                                                              33.8%                                                                              65.51  78.50                                      Resin*                                                                        Water      225.617 lbs.                                                                            --     25.73  --                                    (B)  Melamine/   38.837 lbs.                                                                            100%   4.43   15.70                                      Formalde-                                                                     hyde resin                                                                    (Resimine ®                                                               X745)                                                                    (C)  Phenol/     11.650 lbs.                                                                             50%   1.33   2.35                                       Formalde-                                                                     hyde                                                                          Resin                                                                         (Dexter -                                                                     RP-912)                                                                  (D)  defoamer    3.366 lbs.                                                                             100%   0.38   1.36                                       (Surfynol ™                                                                104                                                                      (E)  n-butanol   2.243 lbs.                                                                             --     0.26   --                                    (E)  Lubricant   20.714 lbs.                                                                             25%   2.36   2.09                                       (Michem-                                                                      lube ™ 160)                                                                TOTALS     876.942 lbs.                                                                            --     100.00%                                                                              100.00%                                    (Rounded)                                                                ______________________________________                                         *The acrylic polymer resin component (A) of this example formulation is       similar to that described in Preparation 1 hereinabove except that            onethird less butanol and onethird less Butyl Cellosolve ® organic        solvent were included in the mixture to cook the monomeric components.   

The specific gravity of the formulation as prepared was 1.020. Theweight per gallon was 8.514 lbs. The percent, by volume, of solids was25.36. The nonvolatile materials was 28.21 percent. The average weightper gallon by volume was 8.189 lbs.

It is contemplated that this formulation composition will be diluted, asdesired, prior to its use in metal can coating operations.

I claim:
 1. A metal container adapted for packaging a beverage or a foodproduct having at least one surface thereof coated with an adherentlayer of a coating composition comprising a mixture of(A) from about 10to about 90 percent by weight of an acrylic polymer latex containing anacrylamide or methacrylamide polymer component formed from the followingmonomeric ingredients:

    ______________________________________                                        INGREDIENT         PERCENT BY WT.                                             ______________________________________                                        (1)    styrene         3-10 percent                                           (2)    ethyl acrylate  0-20 percent                                           (3)    butyl acrylate  0-20 percent                                           (4)    methyl methacrylate                                                                           5-8 percent                                            (5)    methacrylate acid                                                                             3-7 percent                                            (6)    C.sub.1 to C.sub.6 -alkyl-                                                                    0.5-3 percent                                                 oxymethyl-                                                                    acrylamide or                                                                 methacrylamide                                                         ______________________________________                                    

based upon the total materials added to the acrylic polymer latexcomponent, in a liquid medium selected from the group consisting ofwater and a mixture of water with an organic liquid solvent to providefrom about 30 to 35 percent by weight of nonvolatile materials in saidpolymer latex component, (B) from about 1 to about 50 percent by weightof the total solids in the composition of a melamine/formaldehyde resin,(C) from 0.5 to 50 percent by weight of the total solids in thecomposition of a base treated phenol/formaldehyde source resincomposition, which phenol/formaldehyde resin has a viscosity of 20seconds maximum using a No. 4 Ford cup viscosity test method, (D) fromabout 0.1 to about 10 percent by weight of a coating polymer compatiblelubricant uniformly dispersible in the total coating composition, (E)from about 0.1 percent to about 5 percent by weight of the total solidsin the composition of a defoamer material selected from the groupconsisting of (1) an alkyl-branched alkynyl diol having from 10 to 20carbon atoms and (2) aliphatic mineral spirits having C₁ to C₁₂-isoparaffinic hydrocarbons, said can coating composition containingtherein sufficient liquid selected from the group consisting of waterand a water/organic liquid solvent mixture to maintain the components(A) to (E) dispersible therein.
 2. The metal container of claim 1,wherein the pH of the coating composition is maintained at from about7.0 to 7.6
 3. The metal container of claim 1, wherein the acrylicpolymer latex of component (A) contains about 30-35 percent ofnonvolatile material and the acrylic polymer thereof contains about

    ______________________________________                                                3.2 percent     ethyl acrylate                                                13.5 percent    butyl acrylate                                                3.0 percent     methyl acrylate                                               5.0 percent     methacrylic acid                                      and     1.5 percent     N-isobutoxymethyl acrylamide.                         ______________________________________                                    


4. The metal container of claim 1, wherein the phenol/formaldehyde resincomponent (C) is one obtained by combining phenol and a formaldehydesource in the presence of an N, N-di-C₁ to C₃ -alkyl-alkanolamine. 5.The metal container of claim 4, wherein the phenol/formaldehyde resincomponent (C) is one obtained by combining phenol and formaldehydesource in the presence of N, N-dimethylethanolamine.
 6. The metalcontainer of claim 1, wherein the coating composition contains fromabout 10 to 50 percent by weight of solids therein, wherein the solidcontent therein contains(A) from abut 60 to 85 percent by weight of theacrylic polymer latex component, (B) from about 15 to 40 percent of themelamine/formaldehyde source resin component, (C) from about
 0. to 20percent by weight of the phenol/formaldehyde resin component; (D) fromabout 1 to 5 percent by weight of the lubricant component, and (E) fromabout 1 to 4 percent by weight of the defoamer component.